1. Field of the Invention
The present invention relates generally to a lapping method and a lapping apparatus for compensating a warp of a work during a lapping process of the work, and more particularly to a lapping method and a lapping apparatus for consecutively compensating the warp of the work while automatically lapping the work.
2. Related Background Art
A magnetic thin film head has hitherto been lapped after forming the magnetic thin film head in, e.g., a process of manufacturing the magnetic head. In this lapping process, heights of a gap and of a magnetic resistance layer of the magnetic thin film head are uniformly lapped.
An accuracy as hyperfine as sub-micron is required of the heights of the gap and of the magnetic resistance layer. The lapping apparatus is therefore required to automatically lap the work at a high accuracy.
FIGS. 17A.about.17B and 18A.about.18D are explanatory views showing a process of manufacturing a composite type magnetic head.
As illustrated in FIG. 17A, rows 101 of a multiplicity of composite type magnetic heads are formed on a wafer 100 by a thin film technology. The composite type magnetic head 101 is composed of a magnetic resistance element and an inductive writing element which are provided on a substrate.
Next, as shown in FIG. 17B, the wafer 100 is cut in strips, thereby forming a row-bar 101. This row-bar 101 is constructed of one row of magnetic heads 102. Further, resistance elements (ELG elements) 102a for a lapping monitor are provided at a left end, a center and a right end of the row-bar 101.
In the magnetic head 102, it is required that a resistance value of a magnetic resistance film of each magnetic head be adjusted to a fixed value. Therefore, a height of the magnetic resistance film is lapped to a fixed value. The row-bar 101 is, however, extremely thin, and a thickness thereof is on the order of, e.g., 0.3 millimeter. Accordingly, it is difficult to directly fit the row-bar to a lap jig. Hence, as shown in FIG. 17C, the row-bar 101 is bonded to a transfer tool 103 by use of a thermal fusion wax.
Then, as shown in FIG. 18A, the row-bar 101 is placed on a lap plate 104 and lapped. At this time, as known from Japanese Patent Application Laid-Open Publication No.2-124262 (U.S. Pat. No. 5,023,991) and Japanese Patent Application Laid-Open Publication No.10-286765, a resistance value of the ELG element 102a of the row-bar 101 is measured throughout the lapping process. Then, the measured resistance value is converted into a height of the magnetic resistance film of the magnetic head 102, and it is detected whether or not the height reaches a target height.
When it is detected through the measurement of the resistance value that the magnetic resistance film is lapped to the target height, the lapping process is terminated. Thereafter, as shown in FIG. 18B, a slider is formed on a lower surface 101-1 of the row-bar 101.
Further, as shown in FIG. 18C, with the transfer tool 103 remaining fitted, the row-bar 101 is cut into each magnetic head 102. Then, as illustrated in FIG. 18D, each magnetic head 102 is taken out while fusing the thermal fusion wax by heating the transfer tool 103.
The row-bar 101 constructed of one row of magnetic heads 102 is formed, and thereafter the lapping process is executed on the unit of the row-bar 101, whereby the magnetic resistance films of the multiplicity of magnetic heads 102 can be lapped at one time.
FIGS. 19A and 19B are explanatory views showing the prior art.
As shown in FIG. 19A, the row-bar 101 is 0.34 mm thick and 1.2 mm wide. As compared with these dimensions, its length is as long as 40.7 mm, and therefore a warp (bend) is easy to occur in a longitudinal direction. So, it is difficult to ensure straightness which is as precise as sub-microns. Namely, there might be an error in a bonding accuracy in a bonding process of bonding the row-bar 101 to the dedicated transfer tool 103. Further, there is also a limit in terms of a bonding surface accuracy of the transfer tool 103. This might become hindrance against uniformization of lapping accuracy especially of the magnetic resistance element.
Such being the case, the following warp compensating method is proposed in the specification of Japanese Patent Application Laid-Open Publication No.10-286765. As shown in FIG. 19B, the warp compensating involves applying a bend pressure to the central position of the transfer tool 103, and making the transfer tool 103 deformed. Therefore, a bending mechanism for applying the bend pressure is provided in the central position of the transfer tool 103.
Then, a warp quantity of the row-bar 101 attached to the transfer tool 103 is detected by an optical method etc. before the lapping process. Subsequently, the bending mechanism bends the transfer tool 103 so that the detected warp quantity comes to zero during the lapping process. This bending mechanism involves the use of a mechanism for converting a quantity of rotation into displacement by utilizing a screw.
There arise, however, the following problems inherent in the prior art.
First, the transfer tool 103 is formed with a hole for fitting to the lap jig. Therefore, when a lapping pressure is applied to the transfer tool, a warp occurs due to the tool hole. That is, when the lapping pressure is applied, a large pressure is generated at both side ends of the row-bar 101, resulting in a difficulty of lapping the central portion of the row-bar 101. If the lapping continues as it is, the lapping pressure of the row-bar becomes constant, and the work is lapped with the warp remaining occurred. The prior art has such a problem that the warp occurred during the lapping process can not be compensated because of using the warp quantity measured beforehand. Further, there is needed a labor for measuring the warp quantity beforehand.
Second, the bending mechanism involves the screw mechanism in the prior art. Therefore, a problem is that it is difficult to compensate a minute quantity of warp. Moreover, when giving a force for rotating the screw, the lap jig for holding the transfer tool rotates. Because of being incapable of controlling this, the lapping accuracy declines. Further, an excessive pressure is applied to the lap jig, and consequently a smooth lapping process is hard to attain.